The threat was found in a classroom around 10:30 a.m. Thursday, Passaic Detective Andy White said.
"I'll give everyone [x] amount of money if you can find the bomb I hid in the school," it said.
The school was evacuated and Passaic police, the Passaic County Sheriff's Office K-9 unit and bomb squad, and the Passaic County Prosecutor's Office investigated, White said.
Students and staff re-entered the building around 12:20 p.m. after officials deemed it safe, he said.
White said they believed the threat was an isolated incident. Passaic schools received a threatening phone call about gunmen coming to the buildings that caused a lockdown Jan. 26.
The Passaic detecive said they don't know yet when the threat was written on the extension cord but interviewed students and teachers, and checked cameras to find out.
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